1. Field of the Invention
This invention relates to a novel process of manufacturing capacitive devices. The process of this invention is especially useful for manufacturing the capacitive elements of filtered connectors. Another aspect of this invention relates to capacitive devices prepared in accordance with the process of this invention and their use in the manufacture of filtered connectors and other electrical devices which incorporate capacitive devices.
2. Prior Art
Capacitive devices are elements of electrical devices which exhibit the property of a non-conductor that permit the storage of energy as a result of electric displacement when opposite surfaces of the nonconductor are maintained at a difference of potential. Capacitive devices have many uses in electrical circuits. For example, such devices are useful in the construction of capacitor telephones. Moreover, capacitors have also found extensive use in the construction of filtered connectors.
In each of the above-referenced electrical devices, the capacitive device is used to control electromagnetic interference, a problem which is frequently encountered by users of electronic equipment. For example, the receipt and transmission of electromagnetic interference may be reduced or eliminated by utilization of filtered connectors with electronic equipment. Noise, or electromagnetic interference, generated in the circuitry of an electrical device can be deleterious to the operation of other devices if allowed to escape the confines of the device. This problem can be eliminated by shielding the electrical device, connectors and/or cables, and/or by filtering transmission lines.
Filtering is an especially effective way of eliminating the problem, and can be most conveniently accomplished by providing filtering devices at the connection points between the electrical devices. In addition to preventing the out-flow of undesirable signals from a device, the filter also prevents the inflow of such signals to these devices.
In general, filtered connectors can be high pass, low pass or band pass in function. Essentially all conventional filter connectors are based on low pass filters in which a combination of capacitors and inductors provide the filtering function. In these filtered connectors, the circuit usually consists of a capacitor with one plate in electrical contact with a pin, and another plate which contacts the ground. A dielectric material is positioned between the two plates and contacted with same.
Several sub-classes of such capacitance filter connectors are known. One such sub-class is those connectors in which the capacitors are coaxial with the pins. In these connectors, the inner surface of a dielectric cylinder is coated with a conductive material which contacts the pin. The outer surface of the cylinder is similarly coated with a conductive material which contacts the ground plane. Such filter connectors and methods for their manufacture are described in more detail in U.S. Pat. Nos. 4,187,481; 4,198,613; and 3,379,155.
Another sub-class of capacitance filter connectors have been designated planar array ceramic capacitors. Exemplary of this sub-class of connectors are those described in U.S. Pat. Nos. 4,407,552; 4,144,509; and 4,083,022. These connectors consist of ceramic blocks with through holes and capacitors built in the ceramic. Pins are inserted through the holes and electrical contact is made between the pins and metallized pads on the surface of the capacitors. These devices are fairly delicate in that the pins are usually soldered to the pads; and this contact can be easily broken.
The third sub-class of conventional capacitance filter connector are monolithic chip capacitors. In these devices, miniature capacitors in the shape of cubic blocks are inserted into holes in a connector body and electrically contacted with the pin. The opposite end of the block is spring contacted with a ground plane. Illustrative of such connectors are those described in U.S. Pat. Nos. 4,371,226 and 4,376,922. One problem associated with these monolithic chip capacitors is that the monolith is fragile. When these capacitors are subjected to a slight force, a circuit path can be easily broken and a very expensive capacitor plate would have to be discarded. Another disadvantage of this design results from the use of a thin metal film as the ground plane. This thin metal film provides little support for mounting the ceramic monolith. Moreover, the reduced mass of the film and the exposure of only the edges of the film reduces its grounding ability and its impedance characteristics.
Methods heretofore used to manufacture capacitors suffer from a number of inherent disadvantages. One of the most pervasive disadvantage results from the difficulty associated with properly bonding the conductive opposing surfaces to the dielectric material. In one of these known methods, the various elements have been bonded together through use of adhesives, as for example epoxy resins. This procedure greatly complicates the manufacture of the elements and prevents easy automation. Moreover, the use of adhesive leads to the provision of an additional dielectric layer, resulting in an overall increase in the thickness of the capacitor, and giving rise to a decrease in the average dielectric constant of the overall dielectric. Furthermore, the adhesives often do not provide a bond between the metal and dielectric material of sufficient strength.
Thus, there is a need for a method of manufacturing capacitors which allows for easy automation, allows for the manufacture of capacitors of simple design and/or which obviates other disadvantages associated with conventional methods of manufacturing capacitors.